Focus question and advice please!

Started 3 months ago | Questions
JimKasson
JimKasson Forum Pro • Posts: 25,087
Re: The DOF Jedi!

Greg7579 wrote:

That is very well said Jim.

You mean Rick?

Jim

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Greg7579
Greg7579 Senior Member • Posts: 6,696
Re: The DOF Jedi!

JimKasson wrote:

Greg7579 wrote:

That is very well said Jim.

You mean Rick?

Jim

Dammit -- that was Rick?  OK.  Props to Rick. That was a good post.  Thought it was Jim.  I'm traveling, and check with the phone when I get Wi-Fi.  I have been known to not know what thread I am on or who I am talking to in these situations.

You, Rick, Erik, Chris, Left Eye and others are all pretty good at this whole focus point DOF MF thing.

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Macro guy
Macro guy Veteran Member • Posts: 3,972
Re: The DOF Jedi!
1

Greg7579 wrote:

JimKasson wrote:

Greg7579 wrote:

That is very well said Jim.

You mean Rick?

Jim

Dammit -- that was Rick? OK. Props to Rick. That was a good post. Thought it was Jim. I'm traveling, and check with the phone when I get Wi-Fi. I have been known to not know what thread I am on or who I am talking to in these situations.

You, Rick, Erik, Chris, Left Eye and others are all pretty good at this whole focus point DOF MF thing.

Greg Johnson, San Antonio, Texas
https://www.flickr.com/photos/139148982@N02/albums

Seems that your Circle of Confusion was too great and you had inadvertently focused on Jim.  And THAT is why you need a depth of field calculator! ^^

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OP mtakeda Regular Member • Posts: 337
Re: Focus question and advice please!

Jim, I am having difficulty in downloading the app you recommend here. I want to have your comments on the app by the name of Setmycamera.

JimKasson
JimKasson Forum Pro • Posts: 25,087
Re: Focus question and advice please!

mtakeda wrote:

Jim, I am having difficulty in downloading the app you recommend here. I want to have your comments on the app by the name of Setmycamera.

I can’t tell enough by looking at the description. As I said earlier, the calculator I recommended is not an app. It’s a website.

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OP mtakeda Regular Member • Posts: 337
Re: Focus question and advice please!

Thank you. Any recommendation from apps?

JimKasson
JimKasson Forum Pro • Posts: 25,087
Re: Focus question and advice please!

mtakeda wrote:

Thank you. Any recommendation from apps?

Yes.

https://itunes.apple.com/us/app/truedof-pro-dof-calculator/id517481814?mt=8

Jim

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OP mtakeda Regular Member • Posts: 337
Re: Focus question and advice please!

Thank you very much.

OP mtakeda Regular Member • Posts: 337
Re: Focus question and advice please!

Ok I purchased the app you mentioned. For my GFX50R CoC is 38micron according to the software and is this reasonable? In the past you mention to input 1micron then I can not raise the aperture beyond f4. Confused.

fcracer Contributing Member • Posts: 936
Re: Focus question and advice please!
2

mtakeda wrote:

Ok I purchased the app you mentioned. For my GFX50R CoC is 38micron according to the software and is this reasonable? In the past you mention to input 1micron then I can not raise the aperture beyond f4. Confused.

If I read Jim’s note in the thread, he said 10-15, not 1.

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OP mtakeda Regular Member • Posts: 337
Re: Focus question and advice please!

Thank you. I think you are right. He said 10. But when I input 10 to DoF pro it sets the max aperture at f5.

pro

JimKasson
JimKasson Forum Pro • Posts: 25,087
Re: Focus question and advice please!

mtakeda wrote:

Ok I purchased the app you mentioned. For my GFX50R CoC is 38micron according to the software and is this reasonable?

If you like blur.

In the past you mention to input 1micron

I don't think I said anything of the kind. 10 um is acceptable blur for critical work, but many scenes, like the one you posted, will need a larger blur circle if diffraction is included.

then I can not raise the aperture beyond f4. Confused.

Jim

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JimKasson
JimKasson Forum Pro • Posts: 25,087
Re: Focus question and advice please!

mtakeda wrote:

Thank you. I think you are right. He said 10. But when I input 10 to DoF pro it sets the max aperture at f5.

See this:

https://blog.kasson.com/the-last-word/choosing-f-stops-and-focus-distance-for-landscapes/

You can find links to all the other posts in that series by scrolling down to the bottom of the page — below the comments — and looking at the pingbacks.

Jim

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Erik Kaffehr
Erik Kaffehr Senior Member • Posts: 2,822
Re: Focus question and advice please!
1

Hi Jim,

The stuff you are sharing is very good. But, it is based on a basic understanding of basic principles of photographic imaging.

Back in 1913, when Oscar Barnack developed the first Leica he counted what kind of resolution was needed to achieve the quality of a printed postcard of that time. He arrived at about 1/1500 of the image diagonal. The original Leica had 24x36 mm image size with a 43 mm diagonal. 43 / 1500 -> 0.028, or something like 0.030 mm, this is the magic number that DoF calculators use.

So, that essentially says that if we photograph a star image, a spot on the sensor 0.03 mm wide would be perceived as sharp.

Now, digital cameras have pixels. Pixels are mostly rectangular. So how large would that pixel be?

Let's calculate the area of the 0.03 mm spot, that would be Pi * (0.03 / 2) ^2 -> 0.000707 square mm.

How large would a pixel be that had the same area? sqrt (0.000707) -> 26.6 microns.

So a 24x36 mm sensor with 27 micron pitch would match Oskar Barnacks criterion.

How many megapixels would that be? The answer is:

24 / 0.027 * 36 / 0.027 / 1e6 -> 1.2 MP. So, we need like 1.2 MP for a postcard size image. That was true in Oskar Barnack's time and it is true in our time.

So, what is different now? Some things, but not much.

If we look at a 'Bluray' movie, it has a resolution of 1920 x 1080 pixels. That is around 2.1 megapixels twice the information Oskar Barnack found 'good enough' back in 1913.

Just to say, most viewers find 24" full HD screens sharp enough. If we judge sharpness on a 24" monitor we see around 2MP. Oskar Barnack's 1500 CoC across the diagonal shake a bit.

But, now we go 40-50 MP on 24x36 mm or 33x44 mm. The old requirements for sharpness are as valid as ever.

Except, we print (or display) large and view close. A 4K 24" monitor will be not more demanding than a full HD (2K) 24 monitor, unless we view it at half distance.

So, now we have high resolution, we need to change the way we see images to make best use of it. The recipe is to print (or display) large and view close.

Once we do it, we also need to change our criteria for good sharpness.

Best regards

Erik

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JimKasson
JimKasson Forum Pro • Posts: 25,087
Re: Focus question and advice please!

Erik Kaffehr wrote:

Hi Jim,

The stuff you are sharing is very good. But, it is based on a basic understanding of basic principles of photographic imaging.

Back in 1913, when Oscar Barnack developed the first Leica he counted what kind of resolution was needed to achieve the quality of a printed postcard of that time. He arrived at about 1/1500 of the image diagonal. The original Leica had 24x36 mm image size with a 43 mm diagonal. 43 / 1500 -> 0.028, or something like 0.030 mm, this is the magic number that DoF calculators use.

So, that essentially says that if we photograph a star image, a spot on the sensor 0.03 mm wide would be perceived as sharp.

Now, digital cameras have pixels. Pixels are mostly rectangular. So how large would that pixel be?

Let's calculate the area of the 0.03 mm spot, that would be Pi * (0.03 / 2) ^2 -> 0.000707 square mm.

How large would a pixel be that had the same area? sqrt (0.000707) -> 26.6 microns.

So a 24x36 mm sensor with 27 micron pitch would match Oskar Barnacks criterion.

How many megapixels would that be? The answer is:

24 / 0.027 * 36 / 0.027 / 1e6 -> 1.2 MP. So, we need like 1.2 MP for a postcard size image. That was true in Oskar Barnack's time and it is true in our time.

So, what is different now? Some things, but not much.

If we look at a 'Bluray' movie, it has a resolution of 1920 x 1080 pixels. That is around 2.1 megapixels twice the information Oskar Barnack found 'good enough' back in 1913.

Just to say, most viewers find 24" full HD screens sharp enough. If we judge sharpness on a 24" monitor we see around 2MP. Oskar Barnack's 1500 CoC across the diagonal shake a bit.

But, now we go 40-50 MP on 24x36 mm or 33x44 mm. The old requirements for sharpness are as valid as ever.

Except, we print (or display) large and view close. A 4K 24" monitor will be not more demanding than a full HD (2K) 24 monitor, unless we view it at half distance.

So, now we have high resolution, we need to change the way we see images to make best use of it. The recipe is to print (or display) large and view close.

Once we do it, we also need to change our criteria for good sharpness.

I can't disagree with any of that.

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Erik Kaffehr
Erik Kaffehr Senior Member • Posts: 2,822
Re: Focus question and advice please!

JimKasson wrote:

Erik Kaffehr wrote:

Hi Jim,

The stuff you are sharing is very good. But, it is based on a basic understanding of basic principles of photographic imaging.

Back in 1913, when Oscar Barnack developed the first Leica he counted what kind of resolution was needed to achieve the quality of a printed postcard of that time. He arrived at about 1/1500 of the image diagonal. The original Leica had 24x36 mm image size with a 43 mm diagonal. 43 / 1500 -> 0.028, or something like 0.030 mm, this is the magic number that DoF calculators use.

So, that essentially says that if we photograph a star image, a spot on the sensor 0.03 mm wide would be perceived as sharp.

Now, digital cameras have pixels. Pixels are mostly rectangular. So how large would that pixel be?

Let's calculate the area of the 0.03 mm spot, that would be Pi * (0.03 / 2) ^2 -> 0.000707 square mm.

How large would a pixel be that had the same area? sqrt (0.000707) -> 26.6 microns.

So a 24x36 mm sensor with 27 micron pitch would match Oskar Barnacks criterion.

How many megapixels would that be? The answer is:

24 / 0.027 * 36 / 0.027 / 1e6 -> 1.2 MP. So, we need like 1.2 MP for a postcard size image. That was true in Oskar Barnack's time and it is true in our time.

So, what is different now? Some things, but not much.

If we look at a 'Bluray' movie, it has a resolution of 1920 x 1080 pixels. That is around 2.1 megapixels twice the information Oskar Barnack found 'good enough' back in 1913.

Just to say, most viewers find 24" full HD screens sharp enough. If we judge sharpness on a 24" monitor we see around 2MP. Oskar Barnack's 1500 CoC across the diagonal shake a bit.

But, now we go 40-50 MP on 24x36 mm or 33x44 mm. The old requirements for sharpness are as valid as ever.

Except, we print (or display) large and view close. A 4K 24" monitor will be not more demanding than a full HD (2K) 24 monitor, unless we view it at half distance.

So, now we have high resolution, we need to change the way we see images to make best use of it. The recipe is to print (or display) large and view close.

Once we do it, we also need to change our criteria for good sharpness.

I can't disagree with any of that.

Thanks Jim!

My point is that you cannot understand the future without understanding the past.

Many of the recommendations, like 0.030 mm CoC are based on the past. There is nothing wrong with that, those recommendations still serve us well.

But, even cell phones are good enough to fulfill those recommendations. I would say that cell phones are just great for 'f/8 at 1/125s and be there' kind of images.

But, if we want to deliver beyond 'f/8 at 1/125s and be there' we need to learn and understand new criteria, leading to new approaches.

Just to say, 'f/8 at 1/125s and be there' has given us a lot of great images, think David Douglas Duncan, Cornell Capa, Elliot Erwitt or Ernst Haas. Well, regarding, Ernst Haas was probably not in the f/8 at 1/125s club...
With the new camera systems, we may be in search of something else, like 'excellence'. Looking at excellence, we may need to reexamine the rules.

Playing the old f/8 at 1/125s rules on modern cameras may be suboptimal use.

Best regards

Erik

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OP mtakeda Regular Member • Posts: 337
Re: Focus question and advice please!

I am quite confused. Do you think, knowing my landscape shots, CoC 38 is happy compromise or do you different number for me? I do not think I can live with F5 which true DOF pro app sets as the max for wider DOF.

JimKasson
JimKasson Forum Pro • Posts: 25,087
Baby steps

mtakeda wrote:

I am quite confused. Do you think, knowing my landscape shots, CoC 38 is happy compromise

No! How many times do I have to say that?

or do you different number for me? I do not think I can live with F5 which true DOF pro app sets as the max for wider DOF.

You seem to want this whole thing spoon-fed to you. That's not the way to learn how to take pictures. Others can supply the science, but you need to figure out what you can tolerate in terms of blur.

Try this experiment.

  1. Find a scene that has a lot of subject matter at a particular distance.
  2. Using your DOF/diffraction app, take pictures with subject blur circles of 2, 5, 8, 12, 16, 20, 30, 40, and 50 um.
  3. Print crops that translate to your chosen print size. Or, what the hey, make prints in your chosen print size.
  4. Evaluate those.
  5. Than decide, situationally, what blur circle diameters you think are excessive.

Jim

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OP mtakeda Regular Member • Posts: 337
Re: Baby steps

Sorry for bothering you by too many naive questions.

JimKasson
JimKasson Forum Pro • Posts: 25,087
Re: Baby steps

mtakeda wrote:

Sorry for bothering you by too many naive questions.

I don’t mind naive questions at all. I do mind your seeming ignoring of my answers.

Run the test I suggested and the scales will be lifted from your eyes.

Jim

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